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Water chemical shift in 1 H NMR of red cells: Effects of pH when transmembrane magnetic susceptibility differences are low
Author(s) -
Larkin Timothy J.,
Bubb William A.,
Kuchel Philip W.
Publication year - 2008
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21546
Subject(s) - chemistry , chemical shift , magic angle spinning , nuclear magnetic resonance , nuclear magnetic resonance spectroscopy , analytical chemistry (journal) , chromatography , stereochemistry , physics
The 1 H magic angle spinning (MAS) NMR spectrum of water in erythrocyte suspensions shows peaks from each of the intracellular and extracellular water pools. The splitting is a true chemical shift and is brought about by the elimination of water exchange under MAS conditions due to physical separation of the two water populations. The size of the chemical shift difference is determined by the concentration of intracellular protein affecting the average extent of hydrogen bonding of water. We present here a model of the chemical shift behavior for water in erythrocytes under normal high‐resolution NMR conditions based on results from MAS experiments on these cells exposed to different pH and osmotic conditions. The model accurately predicts the chemical shift of water for a static sample, and the results demonstrate that in high‐resolution NMR experiments the chemical shift of water will appear to be invariant if differences in magnetic susceptibility across the cell membrane are minimal (<10% of the magnetic susceptibility of water). Thus, changes in the shape and chemical shift of the water resonance are not due to pH changes in the physiological range. The findings are fundamental to an interpretation of the mechanism of chemical shift effects on the water resonance that may occur in functional MRI. Magn Reson Med 59:707–711, 2008. © 2008 Wiley‐Liss, Inc.